A wind turbine (also referred to as a “wind turbine generator” or WTG) is typically equipped with a mechanical brake on its drive train for bringing the rotor of the wind turbine to a standstill and maintaining the wind turbine in a “parked” (i.e., stopped) position. This may be necessary during repair and maintenance operations, for example. Even though many wind turbines include pitching mechanisms that can be controlled to bring their rotors to a standstill (referred to as “idling”), a mechanical brake may still be required for safety reasons such as emergency stops.
Two types of mechanical brakes commonly used are disc brakes and clutch brakes. Disc brakes include a disc coupled to a shaft in the drivetrain and one or more hydraulically actuated calipers configured to apply friction to the disc via brake pads. The friction creates a braking torque that opposes the motion of the disc, thereby slowing the drivetrain and rotor. Clutch brakes include brake pads that are pre-tensioned by springs into a braking position, but compressed air or hydraulic fluid is typically used to act against the springs and release the brake pads.
One of the challenges in designing the hydraulic system for controlling a mechanical brake is to enable quick activation for safety reasons. For example, conventional hydraulic systems for controlling a disc brake typically include supply lines leading to the brake and one or more electrically-actuated valves located in those lines. The lines are maintained with pressurized fluid during normal operation so that the brake is quickly activated when the valves are actuated. Although such a system may provide quick activation of the brake when needed, there is also a risk that the brake may be unintentionally activated when not needed. For example, one of the valves in the supply line leading to the brake may leak. Even a small leak in one of the valves may, over time, cause a pressure buildup to activate the brake.
Additionally, valves in the supply line controlling activation of the brake are typically normally-open valves (i.e., the valves pre-tensioned into an open position). During operation the valves are electrically set into a closed position to prevent the pressurized fluid from increasing pressures at the brake. Power is switched to “off” to open the valves and activate the brake. Because the brake is only activated occasionally, the valves are highly dependent on power being “on”. This arrangement has the potential to create reliability issues.
Therefore, a hydraulic system for controlling the mechanical brake that sufficiently addresses safety concerns and minimizes the risk of unintended activation is highly desirable.